This one was submitted by my friend and colleague Peter Valicek. It was received from Germany from a seller who also had another large diesel of undoubted Czechoslovakian origin.
Peter tells me that although he has not measured the engine, it seems to have a displacement of 3.5 - 4.5 cc. It displays a number of unusual features, including the side-mounted intake and the metal wrap-around tank at the front. The early Czech Super Atoms used such a tank, although that example was made from plastic. The style of radial mounting used is also very typical of Czech engines from the early post-war period.
If anyone can put a name to this engine, please get in touch through the email link provided.